The modern-day problem of urban and suburban traffic congestion is a well-known phenomenon that takes place in countries all over the world. The root of the problem is grounded in the nature of surface travel along predetermined routes. At some point, two such predetermined routes must cross each other, usually at substantially right angles to one another.
At the point of intersection, only traffic flow along one of these routes can proceed at any given time. The common solution for maintaining an orderly flow of traffic has been the traffic light. Such a traffic light alternately signals the traffic along a particular route to proceed for a predetermined time and then to halt, at which time the traffic along the other route is allowed to proceed. This arrangement is further complicated by the need to allot time for some traffic along one route to turn left onto the other route, thereby changing this traffic's direction of travel. During the time in which such turns are being made, the remaining traffic is stationary. The result of having such complicated timing patterns for the signals at a congested intersection is inefficient cross-flow of traffic and long delays as the traffic backs up, for example, during rush hours.
The conventional solution to the problem posed by the crossing of two traffic routes is to elevate one of the routes, allowing the other route to pass underneath. This arrangement is an improvement because it solves the problem of two crossing flows of traffic by allowing both to proceed simultaneously instead of alternately. Thus, more time is allotted for the flow along each route, thereby allowing an increased volume of traffic along each route.
The elevation of one of the routes does not solve the problem presented, however, by traffic that flows along one route and then turns left onto the second intersecting route. For example, turning vehicles traveling along the non-elevated or ground route must exit, proceed up a graded ramp, halt at the point of entry of the elevated route or overpass, and await a signal before proceeding to turn left onto the elevated route. Likewise, turning vehicles traveling along the elevated route must halt at the point of exit of the elevated route, await a signal before turning left, and then proceed down a graded ramp and onto the non-elevated route. All vehicles as a result must await the precedence indicated by traffic signals. Naturally, because all traffic is not moving simultaneously, such elevated bridges fail to eliminate the stoppages and delays attributable to traffic congestion.
The above-noted problem is in turn solved by the diamond- or clover-shaped interchange. According to the clover-shaped arrangement, for example, vehicles which are proceeding along the unelevated route and which wish to turn left onto the elevated route must turn right and exit up a graded ramp which has a loop configuration. The exiting vehicle approaches this point of exit after passing under the elevated bridge of the crossing route. After exiting, the vehicle proceeds along the looped ramp, which connects the point of exit of the unelevated route with the point of entry of the elevated route. At the point of entry onto the elevated route, the vehicle merges into the traffic flow along the elevated route without coming to a halt. According to such a clover-shaped arrangement, all traffic moves continously and simultaneously.
This type of traffic flow distribution interchange is disadvantageous, however, in that the interchange configuration requires a large amount of land area and thus, is costly to construct. For example, the loops comprising the clover-shaped interchange have a large radius, utilize large amounts of construction materials, and require expensive grading and excavation. Therefore, diamond-and clover-shaped interchanges are unsuitable for use in the confined areas typical of metropolitan environments.